Height ratios for a transition piece of a combustor

ABSTRACT

Provided is a combustor connection structure in which a cross-sectional area (Dout) of a transition piece outlet is set within a range of 0.79≦Dout/Din≦0.9, relative to a cross-sectional area (Din) of a transition piece inlet of a combustor, and in a first stage turbine nozzle of a turbine connected to the transition piece outlet, a size (Hin) in a radial direction between upstream ends of the inner shroud and the outer shroud has a same dimension as a size (a) in a radial direction of the transition piece outlet. In a combustor transition piece that is included in the combustor having a center line (S) arranged with an angle to an axial center (R) of a rotor of a gas turbine and that guides combustion gas to the turbine, a cross-sectional area is monotonously reduced from the transition piece inlet in which the combustion gas flows to the transition piece outlet from which the combustion gas flows out.

RELATED APPLICATIONS

The present application is based on International ApplicationPCT/JP2009/058068 filed Apr. 23, 2009 which claims priority fromJapanese Application Nos. 2008-256531 and 2008-256532 both filed Oct. 1,2008, the disclosures of which are hereby incorporated by referenceherein in their entirety

TECHNICAL FIELD

The present invention relates to a combustor connection structure inwhich the shape of a transition piece outlet of a combustor connected toa turbine is optimized, a combustor transition piece for optimizing theshape of the combustor transition piece in a turbine combustor, adesigning method of such a combustor transition piece, and a gas turbineto which the combustor connection structure and the combustor transitionpiece are applied.

BACKGROUND ART

A gas turbine includes a compressor, a combustor and a turbine. Thecompressor generates high-temperature and high-pressure compressed airby compressing air taken in from an air inlet port. The combustorgenerates high-temperature and high-pressure combustion gas by supplyingfuel to the compressed air and burning them. The turbine includes acasing having an exhaust passage in which a plurality of turbine nozzlesand turbine rotor blades are alternately arranged. The combustion gassupplied to the exhaust passage is used to drive the turbine rotorblades, thereby, for example, rotatably driving a rotor connected to agenerator. The combustion gas having driven the turbine is converted tostatic pressure by a diffuser provided downstream of the turbine andreleased to the atmosphere.

In recent years, combined cycles in which a steam generator and a steamturbine are combined and provided downstream of a gas turbine, forincreasing the temperature of the gas turbine and improving the outputand the efficiency, have been known. Some combined cycles extract steamfrom the steam turbine and cool a combustor in the gas turbine.

To improve the combined efficiency (heat efficiency) in such combinedcycles, it is preferable to reduce the amount of heat exchange to coolat a transition piece outlet of the combustor connected to the turbine.In other words, the heat quantity for cooling the combustor is collectedby steam having performed heat exchange, but if the heat quantity to becooled can be reduced from the beginning, the combined efficiency isimproved. If the flow velocity of the combustion gas is slowed byincreasing the cross-sectional area of the transition piece outlet, theheat-transfer coefficient is also decreased, thereby reducing the amountof heat exchange. However, at a first stage turbine nozzle of a turbinethat is connected to the transition piece outlet and that receives thecombustion gas, the size of the first stage turbine nozzle in the radialdirection provided downstream (outlet side) of the nozzle isaerodynamically determined. Accordingly, a problem arises when thecross-sectional area of the transition piece outlet is increased.

For example, Patent Document 1 discloses a gas turbine in which the sizeof an opening provided upstream of the nozzle in the radial direction islarger than that of the opening provided downstream.

In the above-described gas turbine, the combustion gas of the combustoris supplied to a turbine from the first stage turbine nozzle. Acombustion gas passage is formed in a ring shape, because the firststage turbine nozzle is arranged along the circumference about the axialcenter of the rotor. A plurality of combustors is arranged along thecircumference about the axial center of the rotor to supply combustiongas to the turbine. Ideally, the center line of each of the combustorsis arranged in parallel with the axial center of the rotor, and thecombustion gas is ejected straight to the turbine. However, due tostructural constraints in the gas turbine casing, the center line of thecombustor is obliquely arranged (at least 30 degrees) relative to theaxial center of the rotor, so that the combustion gas is ejectedobliquely from the outside in the radial direction to the inside in theradial direction. In the combustor, high-temperature and high-pressurecombustion gas is produced by taking in compressed air, supplying fuelto the compressed air from a fuel nozzle, and burning them.

For example, as disclosed in Patent Document 2, the combustor includes atransition piece. The transition piece guides combustion gas ejectedfrom the fuel nozzle to a transition piece outlet connected to the firststage turbine nozzle of the turbine from a transition piece inletimmediately after the fuel nozzle. The transition piece is formed tohave a circular cross section of the transition piece inlet, and an arccross section of the transition piece outlet with the ring-shapedcombustion gas passage of the first stage turbine nozzle divided by thenumber of combustors to supply the combustion gas to the first stageturbine nozzle. In other words, the cross-sectional shape of thetransition piece is changed from the transition piece inlet to thetransition piece outlet. To stabilize the flow of the combustion gas,the transition piece needs to be contracted from the transition pieceinlet to the transition piece outlet.

PRIOR ART DOCUMENTS Patent Documents

-   Patent document 1: Japanese Patent Application Laid-open No.    2002-327602-   Patent document 2: Japanese Patent Application Laid-open No.    2006-242559

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

The cross-sectional area of the transition piece outlet may be increasedby employing the configuration of Patent Document 1, aerodynamicallydetermining the size of the opening provided downstream of the firststage turbine nozzle in the radial direction, and increasing the size ofthe opening provided upstream thereof in the radial direction. However,simply enlarging the size of the first stage turbine nozzle in theradial direction on the upstream side increases the cooling area of thenozzle, thereby increasing the amount of cooling air. As a result, thecombined efficiency may be reduced.

The reason why the increase of cooling air reduces the combinedefficiency will now be described. In general, cooling air is obtained bybleeding air compressed by the compressor of the gas turbine, andsending it into the turbine. The compressor of the gas turbine is drivenby a coaxial turbine, but the cooling air does not contribute tocombustion, and therefore, does not contribute much to the work of theturbine. Accordingly, the increased cooling air results in additionalconsumption of the work of the turbine to drive the compressoraccordingly, thereby lowering the output of the gas turbine. Because thetemperature of the cooling air is lower than the temperature of thecombustion gas, if the cooling air is increased, the temperature of theexhaust gas of the gas turbine is further lowered. As a result, theamount of the steam generated by the exhaust gas of the gas turbine isalso reduced. Consequently, if the cooling air is increased, thecombined efficiency is reduced.

The present invention has been made in view of the above circumstances,and intended to provide a combustor connection structure and a gasturbine that can improve the combined efficiency.

As described above, in the combined cycles, the combined efficiency canbe improved if the heat quantity to be cooled is reduced from thebeginning. Accordingly, it has been desired to reduce the amount of heatexchange by reducing the whole flow velocity at the wall surface in thetransition piece of the combustor, preventing a local increase ordecrease of the flow velocity, and reducing the heat-transfercoefficient.

The present invention has been made in view of the above circumstances,and intended to provide a combustor transition piece, a designing methodof a combustor transition piece, and a gas turbine that can optimize theshape of the combustor transition piece and improve the combinedefficiency.

Means for Solving Problem

According to an aspect of the present invention, in a combustorconnection structure, where a cross-sectional area Dout of a transitionpiece outlet relative to a cross-sectional area Din of a transitionpiece inlet of a combustor is set within a range of 0.79≦Dout/Din≦0.9,and a first stage turbine nozzle of a turbine is connected to thetransition piece outlet, an upstream end of an inner shroud that formsan inner wall in a radial direction of the nozzle and an inner end in aradial direction of the transition piece outlet are arranged to contacteach other in an axial direction of a rotor, an upstream end of an outershroud that forms an outer wall in the radial direction of the nozzleand an inner end in a radial direction of the transition piece outletare arranged to contact each other in the axial direction of the rotor,and a size in a radial direction between the upstream ends of the innershroud and the outer shroud has a same dimension as a size in a radialdirection of the transition piece outlet.

In the combustor connection structure, the flow velocity of thecombustion gas at the wall surface is reduced in the transition piece ofthe combustor. Accordingly, the amount of heat exchange at a portion ofthe transition piece outlet is reduced, thereby improving the combinedefficiency. In the turbine, because the flow-in velocity at the upstreamside of the first stage turbine nozzle is reduced, the aerodynamicperformance is improved, thereby improving the combined efficiency. Inthe turbine, because the blade height at the upstream end of the firststage turbine nozzle is increased, the amount of the cooling air to theblade portion is increased. However, because the flow velocity of thecombustion gas at the wall surface is also reduced at the nozzle, theheat-transfer coefficient is reduced. Accordingly, the amount of thecooling air to the whole nozzles does not increase much. Further, thecombined efficiency of the whole gas turbine is improved, because theincrease of the amount of the cooling air is compensated by the improvedaerodynamic performance in the turbine, and because the cross-sectionalarea of the transition piece outlet is determined within an optimalcontraction ratio.

Advantageously, in the combustor connection, the inner shroud isarranged to be in parallel to a shaft center of rotor, and the outershroud is arranged to be oblique to an axial center of the rotor.

In the combustor connection structure in which the center line of thecombustor is obliquely arranged to the axial center, the flow velocityof the combustion gas from the transition piece to the nozzle does notincrease nor decrease. Accordingly, it is possible to reduce the amountof heat exchange, thereby improving the combined efficiency.

According to another aspect of the present invention, in a combustortransition piece that is provided in a combustor having a center linearranged with an angle to an axial center of a rotor of a gas turbineand that guides combustion gas of the combustor to a turbine, across-sectional area is monotonously reduced from a transition pieceinlet in which the combustion gas flows, to a transition piece outletfrom which the combustion gas flows out.

In the combustor transition piece, the change in the cross-sectionalarea from the transition piece inlet to the transition piece outlet isoptimized. The flow velocity at the wall surface from the transitionpiece inlet to the transition piece outlet reaches the peak at thetransition piece outlet. Before reaching the transition piece outlet,the flow velocity is monotonously and stably changed while beingsuppressed so as not to exceed the peak. Accordingly, it is possible toimprove the combined efficiency.

Advantageously, in the combustor transition piece, a cross-sectionalarea Dout of the transition piece outlet is set within a range of0.79≦Dout/Din≦0.9, relative to a cross-sectional area Din of thetransition piece inlet.

In the combustor transition piece, the contraction ratio from thetransition piece inlet to the transition piece outlet is optimized, andthe flow velocity of the combustion gas at the wall surface is reduced.Accordingly, it is possible to reduce the amount of heat exchange at theportion of the transition piece outlet, thereby improving the combinedefficiency.

According to still another aspect of the present invention, a designingmethod of a combustor transition piece includes: setting an angle of acenter line of a combustor relative to an axial center of a rotor of agas turbine; setting a contraction ratio from a transition piece inletin which combustion gas flows to a transition piece outlet from whichthe combustion gas flows out; forming an inner outline in a radialdirection, by extending a straight line in parallel with the center linefrom an inner end in a radial direction of the transition piece inlet toa downstream side, while maintaining a cross-sectional area of thetransition piece inlet, extending a straight line in parallel with theaxial center from an inner end in a radial direction of the transitionpiece outlet to an upstream side, and connecting the straight lines byan arc; forming an outer outline in the radial direction by smoothlyconnecting an outer end in a radial direction on a tubular downstreamside where the cross-sectional area of the transition piece inlet ismaintained, to an outer end in the radial direction of the transitionpiece inlet; and monotonously reducing a cross-sectional area from thetubular downstream side to the transition piece outlet, along the inneroutline in the radial direction and the outer outline in the radialdirection.

In the designing method of the combustor transition piece, it ispossible to form a combustor transition piece in which the change in thecross-sectional shape from the transition piece inlet to the transitionpiece outlet and the shape including the contracting portion areoptimized.

According to still another aspect of the present invention, a gasturbine that supplies combustion gas, obtained by supplying fuel tocompressed air compressed by a compressor and burning the compressed airand the fuel in a combustor, to a turbine to generate rotational power,includes a combustor connection structure, where a cross-sectional areaDout of a transition piece outlet relative to a cross-sectional area Dinof a transition piece inlet of a combustor is set within a range of0.79≦Dout/Din≦0.9, and a first stage turbine nozzle of a turbine isconnected to the transition piece outlet. An upstream end of an innershroud that forms an inner wall in a radial direction of the nozzle andan inner end in a radial direction of the transition piece outlet arearranged to contact each other in an axial direction of a rotor, anupstream end of an outer shroud that forms an outer wall in the radialdirection of the nozzle and an inner end in a radial direction of thetransition piece outlet are arranged to contact each other in the axialdirection of the rotor, and a size in a radial direction between theupstream ends of the inner shroud and the outer shroud has a samedimension as a size in a radial direction of the transition pieceoutlet.

In the gas turbine, the flow velocity of the combustion gas at the wallsurface is reduced in the transition piece of the combustor.Accordingly, the amount of heat exchange at the portion of thetransition piece outlet can be reduced, thereby improving the combinedefficiency. In the turbine, because the flow-in velocity at the upstreamside of the first stage turbine nozzle is reduced, the aerodynamicperformance can be improved, thereby improving the combined efficiency.In the turbine, the blade height at the upstream end of the first stageturbine nozzle is increased, thereby increasing the amount of thecooling air to the blade portion. However, because the flow velocity ofthe combustion gas at the wall surface is also reduced at the nozzle,the heat-transfer coefficient is reduced. Consequently, the amount ofthe cooling air to the whole nozzles does not increase much. Because theincrease of the amount of the cooling air is compensated by the improvedaerodynamic performance in the turbine, and because the cross-sectionalarea of the transition piece outlet is determined within an optimalcontraction ratio, the combined efficiency of the whole gas turbine isimproved. In the structure in which the center line of the combustor isobliquely arranged relative to the axial center, the flow velocity ofthe combustion gas from the transition piece to the nozzle does notincrease nor decrease. Consequently, it is possible to reduce the amountof heat exchange, thereby improving the combined efficiency.

Advantageously, in the combustor connection structure of the gasturbine, the inner shroud is arranged to be in parallel to an axialcenter of the rotor, and the outer shroud is arranged to be oblique tothe axial center of the rotor.

In the gas turbine, in the structure in which the center line of thecombustor is obliquely arranged relative to the axial center, the flowvelocity of the combustion gas from the transition piece to the nozzledoes not increase nor decrease. Accordingly, it is possible to reducethe amount of heat exchange, thereby improving the combined efficiency.

According to still another aspect of the present invention, a gasturbine that supplies combustion gas, obtained by supplying fuel tocompressed air compressed by a compressor and burning the compressed airand the fuel in a combustor, to a turbine to generate rotational power,includes: a combustor transition piece that is provided in the combustorhaving a center line arranged with an angle to an axial center of arotor, and that has a cross-sectional area monotonously reduced from atransition piece inlet in which the combustion gas flows in to atransition piece outlet from which the combustion gas flows out, whilethe combustion gas is guided to the turbine.

In the gas turbine, the change in the cross-sectional area or thecontraction ratio of the combustor transition piece from the transitionpiece inlet to the transition piece outlet is optimized. The flowvelocity of the combustion gas at the wall surface is also reduced fromthe transition piece inlet to the transition piece outlet. Accordingly,the amount of heat exchange can be reduced, thereby improving thecombined efficiency.

Advantageously, in the gas turbine, the combustor transition piece has across-sectional area Dout of the transition piece outlet set within arange of 0.79≦Dout/Din≦0.9, relative to a cross-sectional area Din ofthe transition piece inlet.

In the gas turbine, the contraction ratio of the combustor transitionpiece from the transition piece inlet to the transition piece outlet isoptimized, and the flow velocity of the combustion gas at the wallsurface is reduced. Accordingly, it is possible to reduce the amount ofheat exchange at the portion of the transition piece outlet, therebyimproving the combined efficiency.

Effect of the Invention

In the present invention, the combined efficiency can be improved,because the flow velocity of the combustion gas at the wall surface isreduced by optimizing the shape of the transition piece outlet of thecombustor connected to the turbine, and the amount of heat exchange atthe portion of the transition piece outlet is reduced. In the presentinvention, the combined efficiency can be improved by optimizing thechange in the cross-sectional shape and the contracting portion of thecombustor transition piece from the transition piece inlet to thetransition piece outlet.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic of a gas turbine according to an embodiment of thepresent invention.

FIG. 2 is a schematic of a combustor of the gas turbine.

FIG. 3 is a schematic of an internal shape of a transition piece of thecombustor.

FIG. 4 is a schematic of a contraction ratio of the transition piece.

FIG. 5 is a schematic of an amount of heat exchange in the combustortransition piece relative to a blade height ratio of Hin/Hout.

FIG. 6 is a schematic of an increasing rate of turbine efficiencyrelative to the blade height ratio of Hin/Hout.

FIG. 7 is a schematic of an increasing rate of cooling air to a firststage turbine nozzle relative to the blade height ratio of Hin/Hout.

FIG. 8 is a schematic of an increasing rate of a combined efficiencyrelative to the blade height ratio of Hin/Hout.

FIG. 9 is a conceptual schematic of a designing method of the combustortransition piece.

FIG. 10 is a conceptual schematic of the designing method of thecombustor transition piece.

FIG. 11 is a conceptual schematic of the designing method of thecombustor transition piece.

FIG. 12 is a schematic of a flow velocity near an inner wall surface ofthe combustor transition piece.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

FIG. 1 is a schematic of a gas turbine according to an embodiment of thepresent invention. FIG. 2 is a schematic of a combustor of the gasturbine. FIG. 3 is a schematic of an internal shape of a transitionpiece of the combustor. FIG. 4 is a schematic of the contraction ratioof the transition piece.

A gas turbine, as shown in FIG. 1, includes a compressor 1, a combustor2, and a turbine 3. A rotor 4 is arranged to penetrate through thecenter portions of the compressor 1, the combustor 2, and the turbine 3.The compressor 1, the combustor 2, and the turbine 3 are sequentiallyarranged side-by-side from the upstream to downstream of the flow of airor combustion gas, along a axial center R of the rotor 4. In thefollowing explanation, the axial direction is a direction in parallelwith the axial center R, the circumferential direction is a directionabout the axial center R, and the radial direction is a directionperpendicular to the axial center R. The inside in the radial directionis the side close to the axial center R, and the outside in the radialdirection is the side away from the axial center R.

The compressor 1 produces compressed air by compressing air. Thecompressor 1 includes a compressor casing 12 having an air inlet port 11for taking in air, and a compressor vane 13 and a compressor rotor blade14 are arranged in an air passage in the compressor casing 12. Aplurality of compressor vanes 13 is fixed to the compressor casing 12side, and arranged side-by-side in the circumferential direction. Aplurality of compressor rotor blades 14 is fixed to the rotor 4 side,and arranged side-by-side in the circumferential direction. Thecompressor vanes 13 and the compressor rotor blades 14 are alternatelyarranged in the axial direction.

The combustor 2 generates high-temperature and high-pressure combustiongas, by supplying fuel to the compressed air compressed by thecompressor 1. The combustor 2 includes an inner cylinder 21 in whichcompressed air and fuel are mixed and burned, a transition piece 22 thatguides combustion gas to the turbine 3 from the inner cylinder 21, andan outer casing 23 that covers the outer periphery of the inner cylinder21 and guides the compressed air to the inner cylinder 21 from thecompressor 1. A plurality (16, for example) of combustors 2 is arrangedside-by-side in a combustor casing 24 in the circumferential direction.In each of the combustors 2, due to structural constraints in the gasturbine casing, a center line S of the combustor 2 is obliquely arranged(at least by 30 degrees) to the axial center R of the rotor 4, so as toeject the combustion gas obliquely from the outside in the radialdirection to the inside in the radial direction.

The combustor 2, as shown in FIG. 2, includes a fuel nozzles 251 and 252for mainly supplying fuel. The fuel nozzle 251 is a pilot nozzlearranged in the center of the inner cylinder 21. The fuel nozzles 252are a plurality (eight, for example) of main nozzles arranged adjacentto each other at the periphery of the pilot nozzle 251 in the innercylinder 21 in the circumferential direction. A burner tube 252 b thatcovers each of the main nozzles 252 is arranged at the periphery of themain nozzle 252.

In the combustor 2, as shown in FIG. 2, a flow of high-temperature andhigh-pressure compressed air flows into the outer casing 23, therebyallowing the compressed air to flow into the inner cylinder 21. In theinner cylinder 21, the compressed air is mixed with fuel injected fromthe main nozzles 252, becomes a swirl flow of fuel-air premix in theburner tube 252 b, and flows into the transition piece 22. Thecompressed air is also mixed with fuel injected from the pilot nozzle251, ignited by an ignition device, which is not shown, burned, andejected into the transition piece 22 as combustion gas. At this time,flame holding for stabilizing the combustion of the fuel-air premixsupplied from the burner tube 252 b of each of the main nozzles 252, iscarried out by a diffusion flame generated by the fuel injected from thepilot nozzle 251.

The turbine 3 produces rotational power from the combustion gas burnedin the combustor 2. The turbine 3 has a turbine casing 31 to whichcombustion gas is supplied, and a turbine nozzle 32 and a turbine rotorblade 33 are arranged in an exhaust passage in the turbine casing 31. Aplurality of turbine nozzles 32 is fixed to the turbine casing 31 side,and arranged side-by-side in the circumferential direction. A pluralityof turbine rotor blades 33 is fixed to the outer periphery of a circulardisk about the axial center R of the rotor 4, and arranged side-by-sidein the circumferential direction. The turbine nozzles 32 and the turbinerotor blades 33 are alternately arranged in the axial direction. Anexhaust chamber 34 including a diffuser portion 34 a continuous to theturbine 3 is also provided downstream of the turbine casing 31.

An end of the rotor 4 at the side of the compressor 1 is supported by abearing 41, and an end of the rotor 4 at the side of the exhaust chamber34 is supported by a bearing 42. Accordingly, the rotor 4 is rotatablyarranged about the axial center R. A driving shaft of a generator (notshown) is connected to the end of the rotor 4 at the side of the exhaustchamber 34.

In such a gas turbine, air taken in from the air inlet port 11 of thecompressor 1 becomes high-temperature and high-pressure compressed air,by passing through the compressor vanes 13 and the compressor rotorblades 14, and being compressed. High-temperature and high-pressurecombustion gas is generated by supplying fuel to the compressed air fromthe combustor 2. The combustion gas passes through the turbine nozzles32 and the turbine rotor blades 33 of the turbine 3, thereby rotatablydriving the rotor 4. Electric power is generated by providing rotationalpower to the generator connected to the rotor 4. The combustion gashaving rotatably driven the rotor 4 is converted into static pressure bythe diffuser portion 34 a in the exhaust chamber 34 and released to theatmosphere.

In the gas turbine, as shown in FIGS. 2 and 3, the transition piece 22of the combustor 2 is formed in a tubular shape, and a transition pieceinlet 221 that is an opening at one side is connected to the innercylinder 21, and a transition piece outlet 222 that is an opening at theother side is connected to a first stage turbine nozzle 321 that is anentrance to the exhaust passage of the turbine 3. The inner cylinder 21connected to the transition piece inlet 221 is formed in a cylindershape. Accordingly, the cross-sectional shape of the transition pieceinlet 221 is formed in a circular shape (see FIG. 3). The first stageturbine nozzle 321 connected to the transition piece outlet 222 includesa blade portion 322, and an inner shroud 351 and an outer shroud 352that support the blade portion 322, so as to sandwich the blade portion322 in the radial direction. The inner shroud 351 is an inner wall ofthe first stage turbine nozzle 321 in the radial direction, and theouter shroud 352 is an outer wall of the first stage turbine nozzle 321in the radial direction. A passage of the combustion gas is formed in aring shape along the position of the first stage turbine nozzle 321 inthe circumferential direction. As described above, the combustors 2 arearranged side-by-side in the circumferential direction. Accordingly, thecross-sectional shape of the transition piece outlet 222 is an arc withthe ring shape corresponding to the first stage turbine nozzle 321divided by the number of the combustors 2. In other words, thecross-sectional shape of the transition piece outlet 222 is asubstantially quadrangle shape with an arc portion cut from a fan shape(see FIG. 3). That is, the cross-sectional shape of the transition piece22 is changed from the transition piece inlet 221 to the transitionpiece outlet 222. The circumference of the ring shape of the first stageturbine nozzle 321 connected to the transition piece outlet 222 isalready determined by the aerodynamic shape of the turbine 3.Consequently, the size of the arc cross section of the transition pieceoutlet 222 is determined by dividing the ring shape corresponding to thefirst stage turbine nozzle 321 by the number of the combustors 2.

In the first stage turbine nozzle 321, the size at the downstream sidebetween the inner shroud 351 and the outer shroud 352 in the radialdirection is determined by the aerodynamic shape of the turbine 3. Inthe present embodiment, a size Hout of an opening provided downstream ofthe first stage turbine nozzle 321 in the radial direction (blade heightat the downstream) is the aerodynamically determined size, and a sizeHin between upstream ends of the inner shroud 351 and the outer shroud352 in the radial direction (blade height at the upstream) has a samedimension as a size (a) of the transition piece outlet 222 in the radialdirection. Specifically, the inner shroud 351 is arranged in parallel(including manufacturing error) with the axial center R of the rotor,and the upstream end is arranged to contact with the inner end of thetransition piece outlet 222 in the radial direction, in the axialdirection of the rotor. The upstream end of the outer shroud 352 isplaced to contact with the outer end of the transition piece outlet 222in the radial direction, in the axial direction of the rotor, and thesize Hin of the opening provided upstream in the radial direction (bladeheight at the upstream) is larger than the size Hout of the openingprovided downstream in the radial direction (blade height at thedownstream). Accordingly, the outer shroud 352 is obliquely arrangedwith respect to an axial center of the rotor R so that the openingprovided downstream is gradually widened towards the opening providedupstream.

In the transition piece 22 of the combustor 2, a contracting portion isformed so that the cross-sectional area is reduced from the transitionpiece inlet 221 to the transition piece outlet 222 to stabilize the flowof combustion gas. More preferably, a contraction ratio Dout/Din of across-sectional area Dout of the transition piece outlet 222 relative toa cross-sectional area Din of the transition piece inlet 221 is 0.9. Inother words, when the cross-sectional area of the transition piece inlet221 (diameter (b)) is determined, the cross-sectional area (size (a) inthe radial direction) of the transition piece outlet 222 is determinedby the contraction ratio. As shown by the solid line in FIG. 4, a rangeof the diameter (b) of the transition piece inlet 221 is set, and aratio of the size Hin of the opening provided upstream of the firststage turbine nozzle 321 between the upstream ends of the inner shroud351 and the outer shroud 352 in the radial direction and the size Houtof the opening provided downstream of the first stage turbine nozzle 321in the radial direction is set as a blade height ratio of Hin/Hout withits minimum value X being 1.18, relative to the size (a) of thecross-sectional area Dout of the transition piece outlet 222 in theradial direction of which the contraction ratio is 0.9. Then, as shownby the broken line in FIG. 4, while the minimum value of Hin/Hout of thefirst stage turbine nozzle 321 is X=1.18, the contraction ratio is 0.79when the diameter (b) of the transition piece inlet 221 is maximized.Consequently, a preferable contraction ratio based on the minimum valueX=1.18 of Hin/Hout of the first stage turbine nozzle 321 is a rangewithin 0.79≦Dout/Din≦0.9, within a range of the diameter (b) of thetransition piece inlet 221.

In the combustor connection structure and the gas turbine, in thecombustor 2, the contraction ratio of the size (a) of the transitionpiece outlet 222 in the radial direction relative to the diameter (b) ofthe transition piece inlet 221 is optimized within the range of0.79≦Dout/Din≦0.9. Accordingly, the flow velocity of the combustion gasat the wall surface is reduced, thereby reducing the amount of heatexchange at a portion of the transition piece outlet 222. Consequently,it is possible to improve the combined efficiency.

Because the flow-in velocity at the upstream side of the first stageturbine nozzle 321 is reduced, the aerodynamic performance of theturbine 3 is improved. Accordingly, it is possible to improve thecombined efficiency. In the turbine 3, the blade height at the upstreamside of the first stage turbine nozzle 321 (size Hin provided upstreamof the first stage turbine nozzle 321 in the radial direction) isincreased, thereby increasing the cooling area of the blade portion 322of the first stage turbine nozzle 321. This results in increasing thecooling air and reducing the combined efficiency. However, because theflow velocity of the combustion gas at the wall surface is also reducedin the first stage turbine nozzle 321, thereby reducing theheat-transfer coefficient. Accordingly, the amount of the cooling airdoes not increase much in the whole first stage turbine nozzle 321.Because of the improved aerodynamic performance of the turbine 3, thereduced efficiency described above can be compensated, and because thecross-sectional area of the transition piece outlet 222 is determinedwithin an optimal range of the contraction ratio, the combinedefficiency of the whole gas turbine can be improved.

In the combustor connection structure and the gas turbine, in the firststage turbine nozzle 321 of the turbine 3, the inner shroud 351 isarranged in parallel with the axial center R of the rotor 4, and theupstream end portion of the inner shroud 351 is arranged to contact withthe inner end of the transition piece outlet 222 in the radialdirection, in the axial direction of the rotor. The upstream end portionof the outer shroud 352 is obliquely arranged with respect to the axialcenter R of the rotor (4) so as to contact with the outer end of thetransition piece outlet 222 in the radial direction, in the axialdirection of the rotor. Accordingly, as shown in FIG. 2, in thestructure in which the center line S of the combustor 2 is obliquelyarranged to the axial center R, the flow velocity of the combustion gasto the first stage turbine nozzle 321 from the transition piece 22 doesnot increase nor decrease. Accordingly, the amount of heat exchange canbe reduced, thereby improving the combined efficiency.

These will be described with reference to FIGS. 5 to 8. FIG. 6 is aschematic of a relationship between the ratio of the size Hin betweenupstream ends of the inner shroud 351 and the outer shroud 352 in theradial direction and the size Hout of the opening provided downstream inthe radial direction (blade height ratio of Hin/Hout) of the first stageturbine nozzle 321, and the turbine efficiency. As shown in FIG. 6, theturbine efficiency is improved with the increase of Hin/Hout ratio.

FIG. 7 is a schematic of a relationship between the blade height ratioof Hin/Hout and the increasing rate of the amount of the cooling air tothe first stage turbine nozzle 321. In the diagram, the thin broken lineis the amount of the cooling air to the blade portion, the bold brokenline is the amount of the cooling air to the shroud portion, and thebold solid line is the total amount of the cooling air. As shown in FIG.7, with the increase of Hin/Hout ratio, the cooling area of the bladeportion is increased, thereby increasing the amount of cooling air.However, because the flow velocity of the combustion gas at the wallsurface is reduced, the heat-transfer coefficient is also reduced,thereby reducing the amount of the cooling air to the shroud.Accordingly, the total amount of the cooling air does not increase much.

FIG. 5 is a schematic of a ratio of the amount of heat exchange in acombustor transition piece relative to the blade height ratio ofHin/Hout. As shown in FIG. 5, when the outer shroud is not obliquelyarranged with respect to the axial center R of the rotor (4), in otherwords, based on Hin/Hout=1, the amount of heat exchange is reduced withthe increase of Hin/Hout ratio.

FIG. 8 is a schematic of a relationship between the blade height ratioof Hin/Hout and an increased amount of the combined efficiency. In thediagram, the thin broken line is the sensitivity of the turbineefficiency, the bold broken line is the sensitivity on the amount of thecooling air of the turbine nozzle, and the thin dashed-dotted line isthe sensitivity on the amount of heat exchange of the combustortransition piece. As shown in FIG. 8, when the blade height ratio isincreased, the amount of the cooling air is increased, thereby reducingthe combined efficiency. However, because the turbine efficiency isimproved, the amount of heat exchange in the combustor transition pieceis reduced, thereby improving the combined efficiency as a whole.

FIGS. 9 to 11 are conceptual schematics of a designing method of thetransition piece. FIG. 12 is a schematic of a flow velocity near theinner wall surface of the transition piece. Internal shapes of thetransition piece 22 are shown in FIGS. 9 to 12.

In the designing method of the transition piece 22, as shown in FIG. 9,the angle of the center line S of the combustor 2 is set to the axialcenter R of the rotor 4 in the gas turbine. The angle of the center lineS to the axial center R is set to 30 degrees. The axial center R shownin FIG. 9 is a reference line in parallel with the axial center R. Thediameter of the transition piece inlet 221 of the combustor 2 is set inadvance within the above-described predetermined range. Accordingly, aninner end A in the radial direction and an outer end B in the radialdirection of the transition piece inlet 221 are determined.

The cross-sectional area Dout of the transition piece outlet 222 is setwithin the range of 0.79≦Dout/Din≦0.9, relative to the cross-sectionalarea Din of the transition piece inlet 221. The contraction ratio ismore preferably set to Dout/Din=0.9. The size of the arc transitionpiece outlet 222 is already obtained by dividing the ring shapecorresponding to the first stage turbine nozzle 321 by the number of thecombustors 2. Accordingly, when the cross-sectional area Dout isdetermined, the size in the radial direction is also determined. Aninner end C of the transition piece outlet 222 in the radial directionis placed at a location in parallel with the axial center R, to theinner wall (inner shroud 351) of the first stage turbine nozzle 321 inthe radial direction. Consequently, an outer end D of the transitionpiece outlet 222 in the radial direction is determined. To maximize theretention time of the combustion gas in the transition piece 22, inother words, to maximize the internal volume of the transition piece 22,the cylinder-shaped portion from the transition piece inlet 221 ismaximized, and the length of the contracting portion is shortened asmuch as possible. Accordingly, as shown in FIG. 9, a first virtualstraight line 223 in parallel with the center line S is extended fromthe inner end A of the transition piece inlet 221 in the radialdirection towards the downstream side. A second virtual straight line224 in parallel with the axial center R is extended from the inner end Cof the transition piece outlet 222 in the radial direction towards theupstream side. As described above, the size (Hout) of the openingprovided downstream of the first stage turbine nozzle 321 in the radialdirection is the aerodynamically determined size, and the outer wall(outer shroud 352) of the first stage turbine nozzle 321 in the radialdirection is obliquely arranged with respect to the axial center R ofthe rotor (4) towards the outer end D of the transition piece outlet 222in the radial direction, so that the size (Hin) between upstream ends ofthe inner shroud 351 and the outer shroud 352 in the radial directionhas a same dimension as the size (a) of the transition piece outlet 222in the radial direction.

As shown in FIG. 10, the first virtual straight line 223 and the secondvirtual straight line 224 are then connected. Specifically, thecylinder-shaped portion from the transition piece inlet 221 ismaximized, and a circular arc R1 that comes into contact with the firstvirtual straight line 223 and the second virtual straight line 224, andhas a radius as large as possible is set, so that the inner rim of thetransition piece 22 in the radial direction does not expand inward.Accordingly, the inner end A of the transition piece inlet 221 in theradial direction and the inner end C of the transition piece outlet 222in the radial direction are connected with the first virtual straightline 223, the second virtual straight line 224, and the circular arc R1,thereby determining an inner outline of the transition piece 22 in theradial direction. An inner end E in the radial direction and an outerend F in the radial direction of the cylinder-shaped portion of thetransition piece 22 provided downstream are also determined.

As shown in FIG. 11, the outer end F of the cylinder-shaped portion inthe radial direction and the outer end D of the transition piece outlet222 in the radial direction are then connected. Specifically, a straightline extended from the outer end B in the radial direction to the outerend F in the radial direction of the transition piece inlet 221, and theoblique outer wall (outer shroud 352) of the first stage turbine nozzle321 in the radial direction that extends to the outer end D in theradial direction are smoothly connected by two circular arcs, or by twocircular arcs and a straight line. In other words, at the outer end F inthe radial direction, a circular arc R2 which contacts tangentially witha straight line extended from the outer end B in the radial direction tothe outer end F in the radial direction, is provided from the outer endF in the radial direction to a point G. A straight line 225 connected tothe circular arc R2 is extended from the point G towards the downstream.A straight line 226 of the oblique outer wall (outer shroud 352) of thefirst stage turbine nozzle 321 in the radial direction is extended fromthe outer end D in the radial direction towards the downstream. Acircular arc R3 that connects a point H of the straight line 225 and apoint J of the straight line 256 is also set. Accordingly, the outer endF of the cylinder-shaped portion in the radial direction and the outerend D of the transition piece outlet 222 in the radial direction aresmoothly connected, thereby determining the outer outline of thetransition piece 22 in the radial direction.

Finally, the shape from the transition piece inlet 221 to the inner endE in the radial direction and the outer end F in the radial direction isformed in a cylinder shape, and the cross-sectional area of thecylinder-shaped portion is monotonously reduced to the inner end C inthe radial direction and the outer end D in the radial direction of thetransition piece outlet 222, based on the inner outline in the radialdirection and the outer outline in the radial direction.

To manufacture the transition piece 22, for example, the cylinder-shapedportion may be divided into four in the axial direction. The transitionpiece 22 is formed by pressing the divided cylinder-shaped portions, andconnecting them by welding.

In the transition piece 22 of the combustor 2, as shown in FIG. 12, whenthe flow velocity around the inner wall surface of the outer outline inthe radial direction and the inner outline in the radial direction isviewed, in the transition piece 22 (shown by the solid line) of thepresent embodiment, the flow velocity from the transition piece inlet221 to the transition piece outlet 222 reaches a maximum at thetransition piece outlet 222. Before this, the flow velocity ismonotonously and stably increased corresponding to the contraction ratiowhile the flow velocity is being suppressed, so as not to exceed themaximum value. Alternatively, in a comparison example (shown by thebroken line) in which the cross-sectional area is not monotonouslyreduced, the flow velocity from the transition piece inlet 221 to thetransition piece outlet 222 is fast, and changed unstably. Accordingly,the flow velocity reaches the maximum before reaching the transitionpiece outlet 222.

In this manner, in the combustor transition piece and the gas turbine ofthe present embodiment, the change of the cross-sectional area from thetransition piece inlet 221 to the transition piece outlet 222 isoptimized. Accordingly, the flow velocity of the combustion gas at thewall surface is reduced, and the amount of heat exchange at the portionof the transition piece outlet 222 can be reduced. Consequently, it ispossible to improve the combined efficiency. In the designing method ofthe combustor transition piece, it is possible to obtain an optimalshape of the transition piece 22 that can improve the combinedefficiency.

INDUSTRIAL APPLICABILITY

In this manner, the combustor connection structure, the combustortransition piece, the designing method of a combustor transition piece,and the gas turbine according to the present invention are suitable forimproving the combined efficiency.

EXPLANATIONS OF LETTERS OR NUMERALS

-   -   1 compressor    -   2 combustor    -   21 inner cylinder    -   22 transition piece    -   221 transition piece inlet    -   222 transition piece outlet    -   23 outer casing    -   24 combustor casing    -   251 pilot nozzle    -   252 main nozzle    -   252 b burner tube    -   3 turbine    -   31 turbine casing    -   32 turbine nozzle    -   321 first stage turbine nozzle    -   322 blade portion    -   33 turbine rotor blade    -   351 inner shroud    -   352 outer shroud    -   4 rotor    -   Din cross-sectional area of the transition piece inlet    -   Dout cross-sectional area of the transition piece outlet    -   Dout/Din contraction ratio    -   Hin size between upstream ends of the inner shroud and the outer        shroud in the radial direction (blade height at the upstream)    -   Hout size of an opening provided downstream of the first stage        turbine nozzle in the radial direction (blade height at the        downstream)    -   Hin/Hout ratio of the sizes in the radial direction (blade        height ratio)    -   R axial center of a rotor    -   S center line of the combustor

The invention claimed is:
 1. A combustor connection structure, where a cross-sectional area Dout of a transition piece outlet relative to a cross-sectional area Din of a transition piece inlet of a combustor is set within a range of 0.79≦Dout/Din≦0.9, the combustor connection structure having an angle obliquely radially outward to an axial center of a rotor of a gas turbine, and a first stage turbine nozzle of a turbine is connected to the transition piece outlet, wherein an upstream end of an inner shroud that forms an inner wall in a radial direction of the nozzle and an inner end in a radial direction of the transition piece outlet are arranged to contact each other in an axial direction of the rotor, an upstream end of an outer shroud that forms an outer wall in the radial direction of the nozzle and an inner end in the radial direction of the transition piece outlet are arranged to contact each other in the axial direction of the rotor, a size in a radial direction between the upstream ends of the inner shroud and the outer shroud has a same dimension as a size in the radial direction of the transition piece outlet, wherein the first stage turbine nozzle has an inlet height Hin and an outlet height Hout, and wherein the ratio of Hin/Hout is at least 1.18.
 2. The combustor connection structure according to claim 1, wherein the inner shroud is arranged to be in parallel to the axial center of the rotor, and the outer shroud is arranged to be oblique to the axial center of the rotor.
 3. A combustor transition piece that is provided in a combustor having a center line arranged with an angle obliquely radially outward to an axial center of a rotor of a gas turbine and that guides combustion gas of the combustor to a turbine, wherein a cross-sectional area is monotonously reduced from a transition piece inlet in which the combustion gas flows, to a transition piece outlet from which the combustion gas flows out, and a first stage turbine nozzle of said turbine is connected to said transition piece outlet such that a size in a radial direction of an upstream end of the first stage turbine nozzle has a same dimension of the size in the radial direction of the transition piece outlet, wherein the first stage turbine nozzle has an inlet height Hin and an outlet height Hout, and wherein the ratio of Hin/Hout is at least 1.18.
 4. The combustor transition piece according to claim 3, wherein a cross-sectional area Dout of the transition piece outlet is set within a range of 0.79≦Dout/Din≦0.9, relative to a cross-sectional area Din of the transition piece inlet.
 5. A gas turbine that supplies combustion gas, obtained by supplying fuel to compressed air compressed by a compressor and burning the compressed air and the fuel in a combustor, to a turbine to generate rotational power, the gas turbine comprising: a combustor connection structure, where a cross-sectional area Dout of a transition piece outlet relative to a cross-sectional area Din of a transition piece inlet of the combustor is set within a range of 0.79≦Dout/Din≦0.9, the combustor connection structure having an angle obliquely radially outward to an axial center of a rotor of the gas turbine, and a first stage turbine nozzle of the turbine is connected to the transition piece outlet, wherein the first stage turbine nozzle has an inlet height Hin and an outlet height Hout, and wherein the ratio of Hin/Hout is at least 1.18, wherein an upstream end of an inner shroud that forms an inner wall in a radial direction of the nozzle and an inner end in a radial direction of the transition piece outlet are arranged to contact each other in an axial direction of a rotor, an upstream end of an outer shroud that forms an outer wall in the radial direction of the nozzle and an inner end in the radial direction of the transition piece outlet are arranged to contact each other in the axial direction of the rotor, and a size in the radial direction of the nozzle between the upstream ends of the inner shroud and the outer shroud has a same dimension as a size in the radial direction of the transition piece outlet.
 6. The gas turbine according to claim 5, where, in the combustor connection structure, the inner shroud is arranged to be in parallel to the axial center of the rotor, and the outer shroud is arranged to be oblique to the axial center of the rotor.
 7. A gas turbine that supplies combustion gas, obtained by supplying fuel to compressed air compressed by a compressor and burning the compressed air and the fuel in a combustor, to a turbine to generate rotational power, the gas turbine comprising: a combustor transition piece that is provided in the combustor having a center line arranged with an angle obliquely radially outward to an axial center of a rotor, and that has a cross-sectional area monotonously reduced from a transition piece inlet in which the combustion gas flows in to a transition piece outlet from which the combustion gas flows out, while the combustion gas is guided to the turbine, a first stage turbine nozzle of said turbine is connected to said transition piece outlet such that a size in a radial direction of an upstream end of the first stage turbine nozzle has a same dimension of a size in the radial direction of the transition piece outlet, wherein the first stage turbine nozzle has an inlet height Hin and an outlet height Hout, and wherein the ratio of Hin/Hout is at least 1.18.
 8. The gas turbine according to claim 7, wherein the combustor transition piece has a cross-sectional area Dout of the transition piece outlet set within a range of 0.79≦Dout/Din≦0.9, relative to a cross-sectional area Din of the transition piece inlet. 